The Kuiper Belt

The Kuiper Belt is a region of space along the ecliptic outside the orbit of
Neptune. It contains countless comets and "super comets" or planetesimals. It's
existance was predicted in 1951 by Gerald Kuiper, for whom the belt was named.

Starting in March 1992, and in rapid succession thereafter, a series of icy
planetesimals, or "super comets" have been discovered orbiting the sun beyond
Neptune. These bodies fall into two distinct groups, those having eccentric
orbits syncronized at a 3:2 ratio with the orbital duration of Neptune's and
those having a larger, more circular orbit. Considering Pluto's small size
(smaller than the earth's moon) it should not be considered a planet but the
largest known member of the Kuiper Belt. It is interesting to note that Ceres,
the largest main belt asteroid is more massive than Pluto. This is due to
composition. Ceres is mostly iron and rock while Pluto is made up of mostly
ices.

In addition to these Kuiper Belt objects, also known as Transneptunian,
asteroids, another group of objects orbit the sun among the giant planets of
the outer solar system. These objects, known as Centaur Objects, are most likely
former Kuiper Belt objects. The low points of their orbits have fallen deep into
the outer solar system much like the near earth asteroids have fallen into the
inner solar system from their original orbits in the asteroid belt between Mars
and Jupiter. Some of these objects have had their orbits futher modified by the
giant planets' gravity fields with their high points now also lowered. Chiron,
discovered in 1978, is an example of one of these objects. If one of these
objects were to fall into the inner solar system it would be awe inspriring.
These bodies are much larger than the major comets seen in historical time.

In addition to plenetesimals discovered in the Kuiper Belt, the Hubble Space
Telescope has taken a pair of images of a tiny portion of the belt. By comparing
these pictures using statistical analysis, about 30 object the size of comets we
are used to seeing have been detected. This verifies the other part of Gerald
Kuiper's theory: that the Kuiper Belt was the source of the periodic comets that
dazzle us as they pass through the inner solar system.